Geo-synchronous Earth-Orbit (GEO) spacecraft operators generally desire to maximize spacecraft payload performance and minimize launch cost. One way to reduce launch cost is to launch multiple spacecraft on a single booster. Existing dual-launch methods for GEO spacecraft involve vertically stacked spacecraft configurations that impose constraints on the size of each individual spacecraft and the types of payloads that can be accommodated. The limitations include the aperture size and focal lengths of antennas on each spacecraft, the number of antennas on each spacecraft, and the ability to accommodate other types of payloads such as earth-observing instruments.
FIG. 1A shows an Ariane 5 dual-launch configuration using a SYLDA 5 payload dispenser that partitions the fairing volume into two segments, a lower position and an upper position. FIG. 1B shows two spacecraft arranged in the Ariane 5 dual-launch configuration. The SYLDA 5 encapsulates a lower spacecraft 105 and provides structural support for an upper spacecraft 110. The SYLDA 5 is generally heavy and expensive. The increased mass limits lift capability available to payload. Despite the fact that two spacecraft can be launched together, Ariane 5 launches are still relatively expensive, and an efficient method is needed for launching two GEO communications spacecraft in either the lower or upper position, thereby permitting Ariane 5 to carry three or four spacecraft on a single launch.
In general, Ariane 5 is less efficient and more costly because the Ariane 5 uses a SYLDA to facilitate dual launch in a stacked configuration. This inefficiency has given rise to the stacked configuration where an upper spacecraft is directly attached to a lower spacecraft, as shown for example by the Falcon 9 and Proton stacked dual launch. By attaching the upper spacecraft directly to the lower spacecraft, the need for a SYLDA can be avoided, where, once again, the SYLDA is heavy and expensive and the increased mass from the SYLDA reduces the launch vehicle payload lift capability to the GEO transfer orbit.
Table 1 shows different SYLDA 5 types and corresponding values for heights H1, H2, and H3, as labeled in FIG. 1A, for the different SYLDA 5 types.
TABLE 1Different SYLDA 5 types and corresponding height dimensions.SYLDA 5H1H2H3Type(mm)(mm)(mm)K+2100533364003649A+1500473358004249B+1200443355004549C+900 413352004849D+600 383349005149E+300 353346005449FReference323343005749
A stacked dual-launch configuration for medium-class GEO spacecraft on Falcon 9 has been provided, where an upper spacecraft mounts to an adaptor on the earth deck of a lower spacecraft. FIG. 2A shows a cross-section of a Falcon 9 stacked dual-launch system, which carries two stacked spacecraft 205 and 210. Characteristics of a representative stacked dual-launch spacecraft design of FIG. 2A are shown in Table 2 and Table 3.
TABLE 2Payload accommodations for stacked dual-launchconfiguration.MassUp to 500 kgRepeaterC-band, Ku-band, Ka-bandBandsPower3 kW to 7.5 kW end of life (EOL) payloadpowerFlexible2-4 deployed antennas & option for nadirPayloadsmount; adaptable to support GFE & CFEpayloadsInterfacesSpaceWire, RS422, 1553
TABLE 3Bus specifications for stacked dual-launch configuration.Size1.8 m × 1.9 m × 3.5 m tallMassUp to 1900 kg (wet, including payload)Power3 kW-7.5 kW for payload (total, EOL)BatteryLi-IonDelta-VGTO-GEO transfer (up to 400 kgpropellant)Life15 year service lifeControlZero-momentum, 3-axis
FIG. 2B shows a cross section of a Proton-M dual-launch configuration, which carries two stacked spacecraft 255 and 260. The stacked arrangement is similar to that shown with reference to FIG. 2A.
In each of FIGS. 1A, 1B, 2A, and 2B, because the spacecraft are vertically stacked, the height of each spacecraft is highly constrained. The height constraint limits antenna aperture sizes and focal lengths that can be utilized with each spacecraft. This is a significant drawback if large aperture and high focal length antennas are needed to meet payload performance requirements.
Furthermore, the lower position spacecraft cannot have earth-deck mounted antennas or other types of payloads such as earth-observing instruments, which in general reduces the commercial value of the spacecraft. In practice, these limitations may make it difficult to configure a spacecraft for a given mission or find co-passengers necessary to carry out a stacked dual launch.
For the Falcon 9 and Proton-M 5-m fairings, shown respectively in FIGS. 2A and 2B, the maximum stacked-launch spacecraft height compatible with both launch vehicles may be limited to about 3.5 m, which is also listed in Table 3 with reference to Falcon 9. Because the spacecraft serves as a metering structure for east and west (side-mounted) offset-fed antennas, the focal length of these antennas is generally limited by the height of the spacecraft. It may be possible to achieve longer focal lengths using folded-optics antennas (e.g., Gregorian designs). However, the folded-optics antennas have higher cost due to the need for sub-reflectors and additional deployment mechanisms.
As an example, assuming a focal-length-to-diameter ratio (F/D), also referred to as an f-number, of 1.4, the largest aperture size of the antenna that can be accommodated on a 3.5 m spacecraft is about 2.5 m. Spot-beam missions, however, may require larger aperture sizes, such as aperture sizes between 3 m and 5 m, for example, which could dictate a focal length of up to 7 m. For the upper position of an Ariane 5 with the SYLDA+1500 mm (see Table 1), the spacecraft height for a stacked dual launch would be further limited to about 2.6 m. In this case, the largest aperture size that could be accommodated would be about 1.8 m. For the lower position of the Ariane 5, the short fairing likely makes a stacked configuration for a GEO communications spacecraft impractical.
FIG. 3A shows a vertical cross-section of two Galileo spacecraft 305 and 310 in a side-by-side dual-launch configuration. FIG. 3B shows a horizontal cross-section of the two Galileo spacecraft 305 and 310 in a side-by-side dual-launch configuration. The two Galileo spacecraft 305 and 310 can be in a 4-m Soyuz fairing for example. The Galileo spacecraft, which is a Medium Earth-Orbit (MEO) navigation spacecraft, can be generally categorized as small spacecraft. Example dimensions for the Galileo spacecraft are about 1.1 m (y-axis) and 1.2 m (z-axis) for the lateral dimensions and 2.7 m for the height. Accordingly, the aspect ratio is 0.92. The dual-launch arrangement includes a custom dual-launch adaptor 315 that is sandwiched between the two spacecraft. Because the custom dual-launch adaptor 315 mounts between the two spacecraft 305 and 310, the spacecraft 305 and 310 cannot accommodate payload components such as antennas on both sides.